-LRB- CNN -RRB- -- The Japanese government has criticized former Prime Minister Yukio Hatoyama 's acknowledgment of a `` territorial dispute '' with China over islands in the East China Sea , with the defense minister going so far as to use the word `` traitor . ''

On his four-day private visit to China , Hatoyama told reporters in Beijing on Wednesday , `` The Japanese government says there are no territorial disputes -LRB- between the two countries -RRB- . But if you look at history , there is a dispute . ''

The remarks contradict his own government 's position of indisputable territorial sovereignty over the islands that it calls Senkaku and that China calls Diaoyu .

`` If his -LRB- Hatoyama 's -RRB- remarks have been politically used by China , I 'm unhappy , '' Japanese Defense Minister Itsunori Onodera said on television Thursday . `` At that moment , the word of ` traitor ' arose in my mind . ''

Dangerous waters : Behind the islands dispute

The day after his controversial remarks , Hatoyama , 66 , and his wife visited the Nanjing Memorial , which is for the estimated 300,000 people killed in a 1937 massacre by Japanese forces .

He is the third former Japanese prime minister to visit the memorial , following predecessors Toshiki Kaifu and Tomiichi Murayama . The tribute for Chinese victims stands in contrast to visits by Japanese officials , including Prime Minister Shinzo Abe and predecessor Junichiro Koizumi , to the controversial Yasukuni Shrine in Tokyo , which is dedicated to Japan 's war dead , including war criminals .

`` In the eyes of the Chinese public , -LRB- Hatoyama 's -RRB- visit is very valuable and undermines those in China who argue that all Japanese suffer from amnesia about wartime misdeeds , '' said Jeff Kingston , director of Asian studies at Temple University Japan .

`` I think this mission is an effort by him to introduce a different tenor into bilateral relations , to show it 's not all about saber-rattling , '' he added .

Chinese media extensively covered Hatoyama 's `` apology for Japan 's wartime crimes , '' with pictures of the Hatoyamas bowing and paying silent tribute at the site .

On social media , the visit triggered wide discussions . According to an online poll by Phoenix Online -LRB- iFeng -RRB- , 80 % of the more than 222,000 people who voted said Hatoyama 's visit did not have much political significance , as compared with German Chancellor Willy Brandt 's kneeling before the Warsaw Ghetto Memorial in 1970 .

In another question , nearly two-thirds of 140,000 people surveyed said the visit by a former leader would n't set an example for a fellow Japanese politician .

CCTV commentator Yang Yu , however , praised Hatoyama and urged the Chinese to `` remember the unusual kindness due to its scarcity , '' saying via Weibo , the microblogging site , `` We have reprimanded Japan too many times for not acknowledging the massacre . ''

The official account from Xinhua , China 's state-run news agency , warned that the nationalism of people who `` scold any Japanese they see ... is in fact leading the country to distress . ''

An editorial by the government-run Global Times said that `` China should n't change its policy to Japan just because Hatoyama , a politician currently out of office , gave a few words of friendship . ''

Grievances over World War II atrocities added fuel to violent anti-Japanese protests in China in September , particularly on the anniversary of the 1931 Japanese invasion of China .

And it is not a coincidence , Kingston said , that a Chinese plane entered airspace over the disputed islands -- prompting Japan to scramble fighter jets -- on December 13 , the 75th anniversary of the massacre . It was the first time that the territorial dispute involved planes .

`` The next day on the front page of the newspapers were the images of the -LRB- Nanjing -RRB- Memorial ceremony and the planes , '' Kingston said .

The dispute over the islands stems from 1895 , when , at the end of the Sino-Japanese war , Japan annexed them . China has said that the islands have been its territory for the last five centuries .

CNN 's Steven Jiang and Dayu Zhang in Beijing and Junko Ogura in Tokyo contributed to this report .

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Hatoyama contradicts Japan 's position of indisputable territorial sovereignty over islands

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Japan calls disputed islands Senkaku ; China claims them as `` Diaoyu ''

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Hatoyama and his wife visited the Nanjing Memorial for victims of 1937 massacre

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Chinese media covered extensively his `` apology for Japan 's wartime crimes ''